(1) Field of the Invention
The present invention relates to a polymer-type photoconductive material for electrophotography, which is effectively used as an electrophotographic photosensitive material or a photoconductive toner.
(2) Description of the Related Art
As a practical material comprising an organic photoconductive compound, there can be mentioned a photosensitive material for telectrophotography.
Polymeric photoconductive compounds such as polyvinyl carbazole (PVCz) and low-molecular-weight photoconductive compounds such as hydrazone derivatives are known as the organic photoconductive compound to be used for a photosensitive material for electrophotography.
Known photoconductive polymers such as PVCz have no conductivity to visible rays, and low-molecular-weight photoconductive compounds such as hydrazone compounds do not generate carriers under visible rays and therefore, they cannot be used singly as the photosensitive material. Accordingly, there has been adopted a method in which these low-molecular-weight photoconductive compounds are combined with charge-generating pigments to produce a sensitivity to rays of the visible region. Therefore, in order to obtain a photosensitive material for electrophotography by using a low-molecular-weight photoconductive compound as mentioned above, it is necessary to disperse a charge-generating pigment in a binder polymer.
It is very difficult to disperse a pigment, generally insoluble in a solvent, homogeneously in a binder polymer, and even if the pigment can be homogeneously dispersed, the stability of the dispersion is not good.
Furthermore, since the pigment is an agglomerate, differences in preparation of conditions have a great influence on the electrophotographic characteristics of the obtained photosensitive material. Accordingly, in order to eliminate these influences, it is necessary to control the physical properties of the pigment.